Energetic requirements are present in all humans at all times in the form of physical activity levels and basal metabolic rate. Energy constraints can come in the form of a heavy workload, insufficient dietary intake and in women the constraints imposed by pregnancy and lactation. In affluent societies these are relatively easy to accommodate as most people can afford to eat a sufficient amount of food and maintain energy balance.
However, in some societies a great deal of energy expenditure is required in order to produce food that may not be sufficient to balance energy requirements, as well as having to combat seasonal shortages, therefore coping strategies that involve biological and social adaptations are needed to ensure survival. In some areas of the world this makes life a constant up-hill struggle where different energy constraints can have profound effects on morbidity, mortality, fecundity, fertility, body weight, physical work productivity and well-being.
Coping strategies resulting from energy constraints can be viewed as many small alterations in biology and social activity that when accumulated work together to allow people to operate at a more efficient level and utilise the energy that is available effectively. However, many societies do not have energy conservation and acquisition as their first priority as the western scientists who study them do (De Garine & Koppert, 1990: 260).
The type of energetic stress encountered determines the type of biological alterations used, acute energy deficiency and chronic energy deficiency (Panter-Brick, lecture notes). There are also different responses in thin, normal and obese people. The main biological responses can be generalized into four main categories. 1) Reduction in body weight (eg. Small height for age or low weight for height). 2) Reduction in cost of physical activity. ) Hormonal and chemical alterations (Waterlow, 1990: 5). 4) Decrease in BMR (Panter-Brick, lecture notes). These biological changes are combined with behavioural measures such as minimal work during periods of increased energetic stress (seen in pregnant and lactating women), reduction in food consumption and use of famine foods, reliance on social networks, temporary migration or nomadism, and use of religious practices to reduce anxiety and increase well-being (guru and guru walla in Gambia).
For women the main energy constraints in Third World countries are associated with pregnancy and lactation combined with intensive work and under nutrition, these are combated using both biological and social responses. Pregnant and lactating women in many Third World countries have to continue subsistence activities during pregnancy and lactation. Shostak says of ! Kung women in Botswana, “Many women maintain their normal work routines until the day they give birth. Pregnancy is thought as a given; it is ‘women’s work'”. (Shostak, 1990:178 in Panter-Brick & Pollard, 1999: 153)
Women are able to accommodate to this type of energy constraint biologically by reducing resting metabolic rate, reducing progesterone levels and utilizing fat stores gained during pregnancy. An experiment looking at the relationship between gestation period and RMR among well-nourished Swedish women, poor Scottish women and Gambian women showed that the Scottish and Gambian women had overall a lower RMR during pregnancy than the well-nourished women. This equated to a 13% decrease in the cost of pregnancy (Frisancho, 1993: 392).
Increases in physical work show a correlation with decreased levels of female sex hormones such as progesterone, which is related to ovarian function. This means that the greater the level of physical work the more fertility, fecundity and birth rates are affected so that in societies where women carry out intense labour conception probabilities are reduced per menstrual cycle, therefore women are less likely to become pregnant and recovery time between pregnancies is widened through decreased birth rate.
Lese women in the Ituri forest of the Democratic Republic of Congo are engaged in subsistence farming and experience seasonal food shortages, this results in them having much lower progesterone levels than urban women in the USA (Panter-Brick & Pollard, 1999: 147-150). Fat gain during pregnancy is essential for supplying nutrients for lactation in women with energy constraints. In undernourished women in Gambia fat used during lactation is directly related to how much fat has been gained during pregnancy.
In Guatemalan women fat tissue mobilisation supplied all the energetic costs of lactation rather than increases in dietary intake as in well-nourished women (Frisancho, 1993: 393). The effectiveness of these biological responses can be seen in the fact that dietary intake of pregnant and lactating women in Third World countries can be 24% and 34% lower than their western counterparts yet pregnancy is still successful (Frisancho, 1993: 391) Biological responses are more efficient when combined with behavioural change during pregnancy and lactation for women experiencing energetic stress.
Although many women in Third World countries work throughout pregnancy and lactation their work commitments can be manipulated to reduce energy expenditure. Gambian women reduce Seasonality of crops causes energy constraint differentials at different times of the year. Social changes towards a more westernised society have introduced new ways of accommodating seasonal change as well as undermining more traditional coping strategies among the Massa and Mussey of Chad and Cameroon.